The main objectives of our proposal are to: 1) critically assess the therapeutic value of haloperidol on behavior, discrimination learning and stimulus overselectivity in hyper- and normoactive autistic children; 2) correlate bioavailability of haloperidol with behavioral and electrophysiological parameters; 3) parametrically assess patients on baseline in order to establish a more precise diagnosis and possible subgroups. The above will be measured within the context of a within-subjects reversal design. Behavior will be assessed with both objective and subjective rating scales. Learning rates and attention will be evaluated with the use of an automated data collection system. Blood levels of haloperidol will be assessed along with results obtained from a neurometric test battery, axial tomography, electroencephalogram and pre- and perinatal histories of organicity. Short and long term safety of haloperidol in the same subjects will be assessed.